1. Field of the Invention
This invention relates generally to the methods for mixing printing inks and pigments with fluorescence-inducing material and, specifically, to an improvement in the mixing thereof, termed a threshold mixing method, in which the resultant ink/pigment and fluorescence (printing) compound mixture, when applied to a document substrate, will render the document resistant to photocopying. The invention inculcates a pigment-fluorescence mixing technique by which a particular mix threshold will be reached for assuring that a document printed with the mixed print stuff will reflect a significant amount of white light irrespective of the pigments therein, so as to effect a significant degradation in the document's copy, when such copy is produced by a modern photocopy machine.
2. Discussion of Relevant Art
Numerous attempts have been made to literally "blind" a photocopying device, thus preventing the machine from accomplishing its intended purpose. Almost invariably, these attempts have been made in the interest of securing anti-counterfeit protection for a security or face-value document. Today, the greatest need for secure documents is found in finance for security or negotiable paper such as checks, notes, bonds etc.. Various methods for rendering the aforesaid documents resistant to photocopying include the use of different types of substrates (mattes, paper, etc..), different types of printing (pattern, density of ink mixes, etc..) and/or different kinds of inks, dyes or pigments (print stuff). In the first and second of the aforementioned categories, U.S. Pat. No. 4,522,429, issued to Gardner et. al.. in 1985, discloses a means of providing either colored printed information (or a colored matte) that will frustrate photocopying because coloration mixtures are provided which fall within the human eye's reflection spectral response, but not within the spectral response of the photocopy device. Thus, either the printed information and/or the matte may be seen by the human eye in white light, but cannot be detected by a photocopy machine using its normal lighting, detecting and copying protocol.
Yet another method for producing the copy-proof document, but categorized in the latter of the aforementioned groups (variation of print stuffs), is found in the patent issue to LaCapria in 1978, U.S. Pat. No. 4,066,280. In this disclosure, the patentee teaches his method for frustrating a modern color copier by using a printing ink which is specularly reflective through the use of powdered aluminum which is suspended therein. Since a particle of aluminum is reflective of almost all the white light impinging thereon, LaCapria's suspension of aluminum particles in relatively clear varnishes allows one to see pigmentation included therewith or proximate thereto while providing a high degree of reflectivity to the photocopier illumination. Such a device imparts "flare" to the document (flare is excessive lightening of the images).
The disadvantages to the above-mentioned patent methods and articles are apparent, rather intuitively. In patent '429, the common window of pigment reflection/eye response is quite narrow; therefore the printed matter is so light that commonly used security documents, which are generally printed at great expense, would be poor subjects for exploiting the Gardner et. al. technique. In the latter case, +280, the presence of metallic stuff, no matter how minute, in the fountains of printing presses is but the first problem encountered. The more prevalent problem encountered with the (addition of) reflective particulate matter in printing inks would be manifested in the soiling of the document through normal usage and handling, a spoiling of surface reflectivity. Furthermore, the LaCapria technique requires that a security document be completely redesigned, lest a counterfeiter merely copy an unprotected circulation document and acquire "counterfeit-proof" copies by overlaying a counterfeit-copied document with a varnish layer or print containing the particulate of the +280 disclosure. Thus, not only is the production of the LaCapria document expensive from an ink cost standpoint, but also from that of having to change what might already be a well-known and recognized document, for example, a national currency note or traveler's check.
One other recent development has been government use of devices and microprint techniques to frustrate photocopy counterfeiters. Special threads in the document substrate (matte), often included with paper manufacture, are expensive. Microprinting simply does not "alert" the most common victim of counterfeiting--the consumer. Furthermore, all of the aforementioned techniques, and the documents they are used to produce, do not stop counterfeiting as it has always been performed by the veteran counterfeiter, who prefers to make (first) an offset or intaglio plate. To do this, one need only make a "presentable" photograph/photocopy. Thus, anti-copyability of the document must be the tack taken in any scheme to produce copy-proof documents. Therefore, in contrast to the aforementioned methods and articles, I have sought and discovered a new and wonderful means for frustrating the counterfeiting, by photograph and photocopier, of practically any printed document.
As is well known in classical physics, most colors are observed because the objects upon which white light impinges absorb some wavelengths from the white light and reflect others. It is also known that part of the light absorbed actually passes below the surface of the object, at least so far as the surface coloration or pigmentation is concerned, with internal refraction causing certain of the color wavelengths to be retained (absorbed) and others to reemerge, reflectively giving or imparting the "color" to the object. Since the color white reflected from the object's surface is "white light" (containing all the wavelengths of visible light), it follows that, if the reflecting surface can be altered in some way (perhaps by other mechanisms), more white light (or at least more of the wavelengths that would be initially absorbed) could be reflected. This is the operating premise of my invention.
I have found that in certain chemical compositions, it is possible for additives to be combined with conventional inks, pigmentation, toner or the like (to form a "print stuff") so as to effect such a change in reflectivity when illumination is brighter than normal daylight. I make a certain mixture of chemical compositions that manifests a certain effect under one type of light, while it manifests an altogether different effect (on a document) under the light which is generally employed by photocopiers, that is, white light at about 6500.degree. K. The concept of using fluorescence, as either a fluorescent pigment or a separate compound which lends a fluorescent characteristic to a pigment is not new. Indeed, in LaCapria +280, there is disclosed an example in which fluorescent pigment is balanced first with printing media constituents and then mixed in rather high proportion with the powdered aluminum in synthetic alkyd varnish. The final mixture, comprising the print stuff disclosed, contains approximately (by weight) 29-30% fluorescent pigment. However, +280 gives no indication of the degree of fluorescence found in the pigment, only that it is clearly observed fluorescing under an ultraviolet light. It can be masked by the aluminum content or, if used excessively, tends to mask the specular reflection of the aluminum. Thus, it is clear that LaCapria seeks to embody in his inks both specular reflectance and fluorescent characters. I have chosen to rely upon a fluorescence-inducing chemical additive, known in the trade simply as "fluorescence" in such a manner that the characteristic of fluorescence grants nothing in the way of document counterfeit detection in its genuine form while in daylight or normal artifical lighting, but under the photocopier light or photoflood/flash light sources, imparts significant increase in the other wavelengths of light reflected from a document surface. This increase becomes evident to the observer by the production of a "copy" that is obviously bogus. The invalidity of this copy is evidenced by the degradation of copy quality that results from modest to severe (and often, extreme) washout of print stuff coloration or color "skewing" (shift in wavelength). What appeared under normal light (along with its usual ultra-violet component) as a colored printing is copied (under the photo/photocopier light source) as a self-evident color imperfect, washed out (over lightened) and "non-passable" imitation of the genuine document. It is virtually impossible to produce a printing plate from a copy of my invention.
The properties of fluorescence now being well understood in both academia and industry, I will not digress any further thereinto. Suffice to say, however, that I have found generally available fluorescent pigment of both organic and inorganic constituency to be efficacious in the practice of this invention. Briefly, those of biological origin are, among many others, chlorophYll a (Chl a) and many of the chemical species of Chl a (say, the photosynthetic algae comprised mainly of monovinyl Chl a) and related compounds found in autotrophic bacteria, bacteriochlorophylls (Bchl). Quite matter of factly, in plants excitation is generally dissipated in one of two principal activities, fluorescence and/or photosynthesis. There are several known pigments having absorption characteristics, and consequential fluorescence characteristics, and which are generally described as Chl a, Bchl a and b, Chl-650, 660 and the Alcphycocyanins and Phycocyanins. In the inorganic chemical realm, the following are often employed for their ability to fluoresce at the indicated colors: barium silicate-black; cadmium borate-pink; calcium halophosphate-white; calcium silicate-orange; calcium tungstate-blue; strontium halophosphate-cyan; and zinc silicate-green. Not surprisingly, all of the aforementioned materials absorb strongly in the UV wavelength at 253.7.times.10.sup.-9 cm., proximate a strong emission line for a mercurY arc lamp. As most persons have now experienced, most man-made objects fluoresce to some degree in the presence of "black light" (UV). This is not surprising because many of the aforementioned inorganic (and some of the organic) substances are found in everything from modern polymeric articles to white shirts and writing paper, particularly when the latter two have had fluorescent dyes added to them in order to make them appear "whiter" after washing, exposure to air or purely natural circumstances. Yet, aside from the "whitening" or high-lighting ability of certain fluorescents, makers of security documents and face-value documents do not wish to have their paper appearing as "black light posters" which, needless to say, are also produced at rather high cost. Fortunately, the method I have discovered, as well as the article produced thereby, is relatively inexpensive and, for its intended purpose of avoiding reasonably accurate photo/photocopier duplication, very efficacious. The principal reagent to which I will hereinafter refer as "fluorescence" is any of the commercially available fluorescence compounds that are available in either the fluorescent pigment of LaCapria or a relatively colorless fluorescence (which is a dye) used in the printing industry today. Further, I will concentrate more heavily on the aspects of photocopier frustration, but it should be understood, not necessarily to the exclusion of photo(graphic)proofing which is a corallary thereto.